We have already determined that absence of the pineal gland leads to a decline in proliferative activity (DNA synthesis and mitosis) in lens epithelium. An understanding of the mechanisms involved in bringing this about may lead to knowledge about other factors which control cell division in the crystalline lens. By use of the whole-mount technique for preparing lens epithelium, either alone or combined with autoradiography, we wish to learn how permanent these effects of pinealectomy (Px) are, what the effects are of implanting excess pineal tissue, or of surgically manipulating the sympathetic innervation and/or the diencephalic connection of the pineal gland. By combining histological with autoradiographic procedures we intend to determine how Px affects the rate of fibergenesis, one measure of lens growth. As another parameter of lens growth we will determine, by autoradiography and liquid scintillation spectrometry, respectively, how Px effects the incorporation of precursors of RNA and protein synthesis. Additionally, we will establish a system of lens organ culture by which we will be able to test the effects of the pineal, its products (including melatonin) and antagonists of melatonin synthesis (propranolol) directly on lens cell proliferation. This work has implications for such ocular pathologies as senile cataracts and angle-closure glaucoma.